Diurnal variations in plasma neutral amino acid concentrations among patients with cirrhosis: Effect of dietary protein

The effects of protein ingestion on the diurnal rhythms of plasma concentrations of neutral amino acids were evaluated in patients with chronic cirrhosis. Diets containing varying amounts of protein were administered to 4 patients in two 5-day periods. A protein-free diet resulted in decreased levels of all amino acids except tryptophan. The 75g protein diet increased plasma levels slightly during the day. Absolute concentrations of methionine, tyrosine and phenylalanine were significantly elevated over normal subjects. The plasma ratios were similar to those of normal subjects in response to increased protein ingestion. Overall plasma ratios for leucine, isoleucine and valine were below normal in cirrhotic patients. The implications are that uptake of several of the large amino acids by the brain may be altered.